1. Field of the Invention
The present invention relates generally to a scroll compressor for use in, for example, an air conditioner, a refrigerator or the like and, more particularly, to an orbital drive mechanism used in the scroll compressor.
2. Description of Related Art
In view of numerous features including a compact and light-weight construction, a high operating efficiency, a low noise generation and so on, scroll compressors have gained wide market acceptance. The scroll compressor and its operating principle are disclosed in numerous patents and technical literature and are, therefore, well known by those skilled in the art. As an example of the scroll compressor, Japanese Patent Publication (examined) No. 57-49721, published in 1982, discloses a scroll-type fluid machine which makes use of a link-coupled radial follower mechanism for orbiting one of the scroll members relative to the other while defining a plurality of closed working pockets between scroll wraps thereof.
The scroll compressor disclosed in U.S. Pat. No. 4,824,346 includes an eccentric bush mechanism which may be regarded as a developed version of the link-coupled radial follower mechanism.
A conventional scroll compressor of a type utilizing the eccentric bush mechanism is shown in FIG. 6 in a longitudinal sectional representation and reference thereto will now be made for discussion of the prior art.
The conventional scroll compressor shown in FIG. 6 comprises a compressor housing 101 having a rear end portion to which a stationary scroll member 102 in the form of a stationary end plate 103 having a stationary wrap 104 formed on one surface thereof is secured. An orbiting scroll member 106 in the form of an orbiting end plate 107 having an orbiting wrap 108 formed on one surface thereof is accommodated within the compressor housing 101 with the orbiting wrap 108 being in engagement with the stationary wrap 104 of the stationary scroll member 102 to define a plurality of sealed working pockets 105 therebetween. The opposite surface of the orbiting end plate 107 remote from the orbiting wrap 108 is formed with a generally cylindrical boss 109 in which an annular orbiting bearing 110 is disposed. An eccentric bush 111 in the form of a stud shaft or a disc having a substantial wall thickness and having an eccentric hole 112 defined therein is rotatably housed within the cylindrical boss 109 integral with the orbiting end plate 107 through the annular orbiting bearing 110.
A main shaft 114 has one end formed with a driving pin 115 so as to protrude axially from an end face thereof. The driving pin 115 integral with the main shaft 114 is rotatably received in the eccentric hole 112 of the eccentric bush 111 so that, during rotation of the main shaft 114 about its own longitudinal axis, the driving pin 115 undergoes an eccentric motion relative to the main shaft 114 to impart an orbiting motion to the orbiting scroll member 108. The main shaft 114 is adapted to be driven by an external drive source (for example, an automobile engine though not shown) providing a rotary drive force which is transmitted thereto through a drive transmitting element (not shown) such as, for example, an endless belt, by way of an electromagnetic clutch 118. The electromagnetic clutch 118 is mounted on that portion of the main shaft 114 which protrudes outwardly from the compressor housing 1 through an axial seal assembly 117.
In this design, upon rotation of the main shaft 114 and under the influence of a force such as a force developed by the pressure of a gaseous medium being compressed, the eccentric bush 111 swings about the axis of the driving pin 115 along a generally arcuate path. Consequently, the orbiting wrap 108 undergoes an orbiting motion relative to the stationary wrap 104 while maintaining lines of contact therebetween to achieve a radial seal with which the closed working pockets 105 are sealed.
On the orbiting end plate 107, an annular race 119 and a retainer 120, both made of a high hard steel, are arranged and, similarly, an annular race 122 and a retainer 123 are arranged on steps 121 formed in an inner front wall of the compressor housing 101. These races and retainers support a circular row of balls 124 in position without allowing the balls 124 to displace radially and axially, to thereby support a thrust acting on the orbiting end plate 107 and also to constrain the orbiting scroll member 106 to rotate about its own center.
According to the conventional scroll compressor of the structure described hereinabove, the driving pin 115 is fixed in position relative to the main shaft 114 and, by so fixing the position of the driving pin 115, in the event of start-up or an abrupt acceleration of the scroll compressor, an inertia force of the scroll member acts to swing the longitudinal axis of the eccentric bush 111 in such a direction as to separate the stationary and orbiting wraps away from each other to release the closed working pockets 105, to thereby minimize generation of abnormal sounds and/or vibrations.
In addition, although since the eccentric bush 111 is rotatable around the driving pin 115, the radial sealing can be achieved, the angle of rotation resulting from the swinging motion of the eccentric bush 111 must be regulated to eliminate problems associated with interference between the surrounding component parts. For this purpose, a regulating pin 113 protruding axially from the eccentric bush 111 so as to engage loosely in a regulating hole 116 formed in the main shaft 114 with a predetermined gap left between the regulating pin 113 and the wall defining the regulating hole 116 is employed as means for regulating the angle of rotation of the eccentric bush 111.
Considering, however, that in addition to the compact and light-weight construction, the high operating efficiency and the quiet features, the scroll compressor intended particularly for use in an automotive vehicle is required to have a durability against severe operating conditions such as extremely high or low operating speed and/or extremely high or low ambient temperature, the driving pin 115 employed in the conventional scroll compressor of the structure described above poses a problem associated with physical strength thereof. In other words, since the driving pin 115 is eccentrically engaged in the eccentric bush 111 which tends to be manufactured as compact as possible and having a bore size as small as possible, the driving pin 111 is limited in diameter and, therefore, the driving pin 115 of a given diameter must have a sufficient physical strength. In particular where the scroll compressor is operated under a severe condition such as a high-speed, high-load operating condition, there is a relatively high possibility of breakage of the driving pin 115.
In addition, the conventional scroll compressor requires the use of a rotational angle regulating means for regulating the angle of rotation resulting from the swinging motion of the eccentric bush 111 and is, therefore, disadvantageous in terms of manufacturability and manufacturing cost.